1. Field of the Invention
The present invention relates to a machine tool for cutting a workpiece having an inclined surface or curved surface, and a cutting method.
2. Description of the Related Art
A lathe, which is a type of machine tool, holds a workpiece to be machined, on a rotation axis (spindle) and performs cutting or the like on the workpiece using a machining tool such as a cutting tool while rotating the workpiece (see Japanese Patent No. 2701706). For example, when a workpiece having an inclined surface is machined using a lathe including a spindle having a tapered fitting portion, the lathe cuts the workpiece while determining the amount of cutting in accordance with the inclination of the inclined surface and moving the machining tool in the direction of the rotation axis. However, it is difficult to obtain the required surface roughness by simply cutting the workpiece in such a manner. For this reason, the required surface roughness is obtained, for example, by pre-machining the workpiece using the lathe and then finishing it by grinding the inclined surface thereof using an angular grindstone or the like.
However, in order to pre-machine the workpiece using the lathe and then finish it using a grindstone as described above, it is necessary to unload the workpiece from the lathe and then newly set the workpiece on a grinder. Accordingly, the entire machining time is increased. Further, when the workpiece is rotated on the grinder, the amount of grinding when the angular grindstone contacts the workpiece varies between the inner circumference and outer circumference of the inclined surface, since the circumferential velocity varies between the inner circumference and outer circumference of the inclined surface. This may make it difficult to obtain uniform surface roughness, that is, to obtain the required surface roughness.